The present invention relates to a method of removing dirt and oil from surfaces. More particularly, the present invention relates to the use of lipid vesicles or liposomes in a cleaner which can encapsulate the dirt or oil on the surface, thereby removing it.
There are presently two type of detergents used for dirt and oil removal from solid surfaces; the first contain primarily natural or synthetic soaps while the second are the synthetic soapless detergents. Soaps normally consist of sodium or potassium salts of long-chain fatty acids and are now manufactured by saponification of triglycerides from fats with sodium or potassium hydroxide. However, soaps do not function well in acid solutions because of the formation of insoluble fatty acids. In addition, calcium or magnesium ions tend to form a soap scum in the form of an insoluble precipitate. Although additives such as phosphates and sodium carbonate may ameliorate many of these problems, synthetic soapless detergents have been used where soaps are not effective. These synthetic soapless detergents normally have alkyl sulfates, alkyl or aryl sulphonates, or non-ionic polyoxyethylene oxide derivatives as their primary active ingredients.
A good detergent must possess at least three characteristics:
(1) good wetting properties in allow the detergent to contact the surface, PA1 (2) the ability to remove dirt from the surface into the bulk of the liquid, and PA1 (3) the ability to solubilize or disperse the removed dirt to prevent redeposit on the surface, or formation of a scum.
The best wetting agents are those with the shorter fatty acid chains, e.g., C.sub.8 versus C.sub.14 or C.sub.16. However, the longer chain surface active agents appear to provide better stability for the dirt or oil in the bulk solution once it is removed from the surface. Therefore, one of the problems in detergent science is forming the proper balance between the wetting and stabilization properties.
In practice, the detergent or surface active agent changes the contact angle of the dirt or oil on the surface at the triple solid-oil-water interface, reducing the contact angle so that the oil rolls up into a sphere and can be removed. The materials that act as the best detergents are normally those which form micelles and at one time, there was a theory that the micelles were involved in the cleaning action. In recent years, however, it has become clear that it is the free surfactants which do the cleaning, not those in the micelles. It appears that the micelles merely act as reservoirs of the surface active agents. However, although it is not the surfactants in the micelles which provide the cleaning action, the surfactants do not function as satisfactory oil-in-water emulsifiers, e.g., do not act properly in the stabilization step, until the concentration of the surfactant in the aqueous phase exceeds the critical micelle concentration. Accordingly, micelle formation is normally expected in detergents.
In standard detergent action, oil-in-water emulsions are formed to stabilize the oily dirt particles and maintain them in solutions. The surfactants act to lower the surface tension of the water and the interfacial tension between the water and oil. However, there is no true vesicle formation or even micellar entrapment of the dirt using most detergents.
Until the methods and products described in the Previously cited U.S. patent application Ser. No. 157,571, now U.S. Pat. No. 4,911,928, there had been no description of lipid vesicles or liposomes which could encapsulate oil, except for the small amount of lipid which could be incorporated into the lipid bilayers before bilayer breakdown. However, U.S. patent application Ser. No. 157,571, now U.S. Pat. No. 4,911,928, describes paucilamellar lipid vesicles having large amorphous oil-filled centers which could carry substantial quantities of oily material. These vesicles, which have 2-10 lipid bilayers surrounding a large, amorphous central cavity, are stable and can be formed under conditions which are so rapid that they are cost-effective for use in industrial applications.
Accordingly, an object of the invention is to provide a surface cleaning solution which contains lipid vesicles or liposomes.
Another object of the invention is to provide a surface cleaning agent which encapsulates oil or dirt in lipid vesicles to remove it from the surface.
A further object of the invention is a method of cleaning hand using a lipid vesicle skin cleaner to encapsulate grease or dirt.
These and other objects and features of the invention will be apparent from the following description.